This invention relates to a method of protecting machine-readable markings by means of an optically clear, chemically resistant, and mechanically strong coating as well as to articles carrying on their outer surfaces machine-readable markings protected by such coating.
Machine-readable markings are nowadays routinely placed on various objects to provide instant identification of such objects, for example, their nature, price, size, or destination. The most commonly used machine-readable marking is a bar code system, The bar code marking applied to the object is read by a suitable device, which generates a control signal, usually electrical, which is sent to a computer or a computer-controlled apparatus for taking appropriate action. This may be simply entering the information about the object into a database for the purpose of inventory, or directing a manufacturing or processing machine to perform a step in a process, or directing a car or container to the proper destination. Sometimes, machine-readable markings are placed on metal, usually aluminum, tags attached to an object, for example, to a piece of plant or laboratory equipment. Information stored on those tags may, in addition to simple inventory identification, include information about safety or hazards of operation, or maintenance requirements. In other cases, machine-readable markings are often painted on or otherwise applied to the exterior surfaces of shipping containers and railroad freight cars, so that they can be easily identified as to ownership, contents, and destination.
In many applications where machine-readable markings are applied to various objects, the objects themselves are exposed to corrosive environment, for example, in plants or laboratories. In other cases, the objects may be exposed to adverse atmospheric conditions, for example, smog, rain and snow. With time, those markings can become unreadable or inacurate.
It, therefore, is desirable to protect machine-readable markings by means of a coating that can be readily applied, that is transparent to the wavelength used by the contemplated reading device, that is resistant to the corrosive or adverse atmospheric conditions to which the markings may be exposed, and that can be readily cleaned and restored to its original appearance
Various protective coatings have been proposed in the past. Thus, U.S. Pat. No. 4,600,630 to Quinn et al. proposes a coating of a polymeric composition that is curable upon exposure to ultraviolet radiation, and then irradiating the overcoating with ultraviolet radiation to produce a cured, nontacky, light-transmitting film.
U.S. Pat. No. 4,670,295 is a division of the application which resulted in U.S. Pat. No. 4,600,630 and discloses a similar coating.
U.S. Pat. No. 4,066,873 to Schatz is concerned with identification and access cards, especially for banking operations. The purpose of protective coating is to prevent wear and damage of the card in normal use. Transparent acrylic or polyvinyl chloride resins are mentioned as suitable for that purpose.
Finally, a sales bulletin of CHR Industries (407 East Street, New Haven, Conn.) discloses a tape made of an ethylene/tetrafluoroethylene copolymer sold by the Du Pont Company under the trademark T.sup.2 TEFZEL.RTM.. The tape is described as being optically clear and fully "solar and U/V transparent". It is provided with an optically clear acrylic adhesive. Since the copolymer is not readily soluble in organic solvents and, therefore, cannot be applied by spray-coating or dip-coating from a solution, the idea of providing an adhesive-backed tape is a very good one. Still, in many applications, spray-coating or dip-coating, if possible, would be less labor-intensive and, therefore, more economical, and it would be particularly suitable for articles such as identification tags, which could be coated by simple dipping in a polymer solution, as well as for coating large bar codes such as those painted on the outside surfaces of shipping containers and railroad cars, which could be spray-coated. In addition, a clear polymer coating that is not only transparent but also stable to both sunlight and UV radiation and that does not require an adhesive backing, which backing itself may be unstable on prolonged exposure to either sunlight or UV radiation, has the additional advantage of being particularly well suited for outdoor applications.